Ultrasonic systems for carrying out flow measurements in fluids

ABSTRACT

An ultrasonic system for carrying out flowrate measurement in fluids comprises a generator transmitting a frequency modulated wave signal. This signal is converted into an ultrasonic signal by a first transducer. A second transducer, after propagation across the fluid receives this signal, and converts this into a delayed electric wave train. This wave train delivered to a dispersive delay line is transformed therein into a train of very short duration. This latter signal after detection, allows accurate determination of the propagation time across the fluid.

United States Patent Courty Apr. 17, 1973 ULTRASONIC SYSTEMS FOR3,402,606 9/1968 Bruha ..73/194 A CARRYING OUT FLOW 3,440,876 4/1969Hayes et a]. ..73/l94 A MEASUREMENTS IN FLUIDS 3,486,377 12/1969 Franchi..73/290 V [75] Inventor: Albert Courty, Paris, France primary Examinercharles Rueh] [73] Assignee: Thomson-CSF, Paris, France Anomey cushman,Darby & Cushman [21 1 Appl 1 16380 An ultrasonic system for carrying outfiowrate measurement in fluids comprises a generator transmitting [30] Fi A li ti P i i D m a frequency modulated wave signal. This signal isconverted into an ultrasonic signal by a first transducen A Feb. 27,1970 France ..7007i89 Second transducer, after propagation across thefluid th"'al, d rtsth"t d] d [521 user ..73/194A 353 113 31 m 0 a We[51] Int. Cl ..G01f 1/00, GOlp 5/00 [58] Field of Search ..73/194 A, 290V This wave train delivered to a dispersive delay line is transformedtherein into a train of very short duration. [56] References Cited Thislatter signal after detection, allows accurate UNITED STATES PATENTSdetermination of the propagation time across the fluid.

3,336,801 8/1967 Snavely ..73/l89 5 Claims, 4 Drawing Figures .PATENIEDAPR 1 7 I973 SHEET 2 OF 3 BST I LLJ BST PArENr oAPRmsm 3721454 SHEET 3OF 3 E Transmltter gl z L/////////\/ A Generator V21 Receive FTransrmtter Transmrtter D l Receiver Generator [5 ine Lo ii I 1 QBT/nmingvCircuiT p v nwtzvr ra orfi v mutw: rotor r 8ST} Master osciliator I I v ANDgake Y D tCounter C i i a to A I IL]. 4 AND an loooeconverter gate qosc Counter Oscillator I Squaring device ULTRASONICSYSTEMS FOR CARRYING OUT FLOW MEASUREMENTS IN FLUIDS The presentinvention relates to improvements in ultrasonic systems and methods forcarrying out flow measurement in fluids, in particular fluids which areflowing through a pipe.

Ultrasonic techniques involve the measurement of the time of propagationof acoustic waves over one or more trajectories through the fluidconcerned. The measurements can be carried out without contact with thefluid and thus without modifying the flow conditions to which the fluidis subjected.

In prior art systems, even where the signal transmitted through anacoustic trajectory or link across the fluid has a very short duration,the time of arrival of the signal at the receiving end cannot generallybe determined with anything more than mediocre accuracy, as much becauseof the random phenomena as because of the selectivity of thepiezoelectric vibrators (transducers), which are used to convert theelectrical signals into acoustic waves in the fluid, and vice versa. Thesignals received are generally detected in a transient condition bythreshold devices, the inaccuracy being translated into terms offluctuations in the time of clearance of the threshold in these devices.

The system and method in accordance with the invention do not exhibitthese drawbacks since they make it possible to use relatively longsignals which experience virtually no distortion during the acoustictrajectory; moreover, the characteristic measurement times do not occurduring the transient condition of the signals.

According to the invention, there is provided an ultrasonic system forcyclically measuring the flow of a fluid in a pipe, comprising incombination:

first means for repeatedly generating a timing signal at the beginningof each measuring cycle;

second means triggered by said first means for generating a firstelectrical wave train of fixed duration frequency modulated according toa predetermined law between fixed upper and lower frequencies,

at least a first pair of opposed transducer meansfor location onopposite sides of said pipe, including a first transducer for convertingsaid first wave train into a first sound wave and for transmitting saidfirst sound wave along a first path through the fluid within said pipeand a second transducer for receiving said transmitted first sound waveand for converting said received sound wave into a second electricalwave train;

first means for applying said first wave train to said first transducer;

first delay line means having a dispersive delay time versus frequencycharacteristic, fed by said second transducer for converting said secondelectrical wave train into a first compressed one of short duration;

first detector means fed by said first delay line means for delivering afirst compressed pulse in response to said first compressed wave train;

a first bistable multivibrator having a first triggering input forreceiving said timing signal and an output for delivering in responsethereto a non-zero value constant voltage and a second triggering inputfor receiving said first compressed pulse and for delivering at saidoutput in response thereto a zero value voltage,

whereby said first multivibrator output delivers a first rectangularwaveform having a duration equal to the sum of the sound wavepropagation time interval across the fluid between said first and secondtransducersand the constant delay time interval provided by said delayline means.

This and other features of the present invention will become apparentfrom the following description, given by way of example, and withreference to the accom panying drawings in which:

FIG. 1 is the block-diagram of a part of a system in accordance with theinvention;

FIGS. 2 and 3 are diagrams illustrating the waveforms at differentpoints in two systems, one of which being a prior art system and thisother one according to the invention.

FIG. 4 is the diagram of a flowmeter using the system in accordance withthe invention.

FIG. 1 illustrates the diagram of a circuit which incorporates the basicelements used in the system and method of the invention. In this Figureis shown a pipe section 1 through which a fluid F is flowing in thedirection of the arrow. Piezoelectric vibrators Ve and Vr locatedexternally of the pipe or internally thereof, define an acoustictrajectory or link of length L crossing the fluid F the vibrator Veserves to convert an electrical signal into an acoustic wave whichtravels over the trajectory L and the vibrator Vr carries out thereverse conversion. These vibrators are constituted by quartz crystals,ceramic or other piezoelectric plates which are acoustically coupledwith the fluid through the pipe wall which may or may not be thinneddown at the location of the vibrators.

An electrical signal generator G is capable of transmitting a wave trainfrequency modulated according to a predetermined law, and having a fixedduration, the upper frequency and the lower frequency being constant.

This generator G has an input connected to the output ofa timing circuitBT, which generates at predetermined instants, pulses of short duration.

Time circuit BT has another output connected to one of the triggeringinputs of a bistable multivibrator BST, having two stable states, the 0state in which its output voltage has a zero value, the I state, forwhich its output voltage has a constant non-zero value.

Each pulse supplied by the BT timing circuit on the one hand, triggersthe generator G which transmits a wave train and on the other hand,triggers the bistable multivibrator BST from state 0 to state 1.

Generator G is coupled to the transducer Ve by means of a transmitter oramplifier E. The output of. transducer Vr is connected to the input of adispersive delay line LD. The output of this latter line is connected bymeans of a detector D, to the other input of bistable BST.

Bistable BST delivers its output voltage to an input of an AND gate ET,whose other input receives pulses having a fixed repetition frequency,these pulses being generated by a clock H. The output of the AND gate ETis connected to a counter CT.

As shown in FIG. 3, the transmitted ultrasonic wave train K, has aduration T which can be relatively long, Vr and Vc having a band widthincluding the upper and lower frequencies of train K Delay line LD has adispersive delay time versus frequency characteristic such that theinstantaneous frequency occuring at the beginning of the frequencymodulated wave train is delayed more than the one occuring at its end,i.e. it has the effect of shortening the duration of the frequencymodulated wave train applied to its input. If the law, according towhich the wave is frequency-modulated, is adapted to thischaracteristic, the output of the delay line LD will deliver, after adelay time rd of fixed value, a so called compressed pulsed wave trainof very short duration; detector D delivers in response to this wavetrain a pulse for resetting the bistable BST to its state.

The diagrams shown in FIG. 3 explain the operation of the device.

The duration of the square wave voltage delivered by bistable BST isequal to te td,

te being the time elapsed during the propagation of sonic wave train K,from vibrator Ve to Vr and td being the above-mentioned delay time ofLD.

Clock H and counter CT allow the counting of pulses produced within thetime interval te td.

The pulse P delivered by the timing circuit ET is shown in the firstdiagram.

The sonic wave train Ke delivered by Vibrator Ve is a frequencymodulated wave having a duration T and an envelope of substantiallyrectangular shape.

The electrical wave train K, delivered by Vr response to the sonic onereceived has substantially the same wave form, but is delayed by a timete with respect to wave train Ke.

The compressed wave train l delivered by delay line LD has a muchshorter duration than wave train K,; diode D delivers a triggering pulsesimilar to that supplied from BT.

Consequently, the switching times of the bistable BST are determinedwith a very great accuracy.

In the case of FIG. 2 corresponding to a device without delay line, theapplied signal is necessarily a short voltage pulse. Because of naturalphenomena due to the selectivity of the vibrators and the elasticity ofthe fluid, the short signal produces at the output of the vibrator Ve alonger signal whose envelope decays in accordance with an exponentialfunction and then,

after the delay tl resulting from the passage of the acoustic wavethrough the fluid, the signal appearing at the output of the vibrator Vrhas an exponential rise and an exponential decay. This exponential riseof the envelope is an obstacle to a precise resetting (without jitter)of the bistable multivibrator to its initial condition the part of thebistable trigger stage BST and, at

the output of the latter, the duration of the rectangular waveformsignal is equal to the delay tl plus an error interval tx which isdetermined by the instant at which the bistable trigger stage switchesfrom one state to another. This error interval fluctuates because of therandom the rise law of the signal received by Vr and, consequently,because of the uncertainty in the instant at which. the signal exceedsthe threshold value at which the bistable multivibrator can betriggered.

The indication obtained for the velocity of the sound, modified orotherwise by the velocity of the fluid, can be used directly in variousapparatus such as those designed as to detect the fronts definingdifferent products circulating through one and the same pipe, or

to follow the development of or determine the quality of said products.This application is of course in no way limitative of the scope of thisparticular ultrasonic velocity measuring method.

The method and system in accordance with the invention likewise makes itpossible to measure the velocity of flow and flowrate of a fluidcirculating through a pipe, provided that several acoustic trajectoriesare arranged in said pipe. in addition to this absolute measurement, adifferential flow velocity measurement at two points in a pipe can becarried out in order to determine, for example, whether or not there areany leaks in the pipe. This application is equally not limited to thisparticular method of measuring velocity of flow by ultrasonictechniques. The conventional method of measurement of the phase shiftbetween the emitted and received waves, could equally well be employed.

FIG. 4 shows an embodiment which can be, according to the invention usedas a flowmeter, for metering the flowrate of a fluid in a pipe.

This embodiment is made of devices of the type shown in FIG. 1.

It comprises:

a. Two transducers V and V each of which beingboth capable of receivinga sonic wave train and of transmitting the same toward the other. Thesound beams are at an angle 0 with respect to the flow direction.Transducers V and V have their respective inputs connected totransmitter-amplifiers E, and E and their respective outputs connectedto receiveramplifiers R and R Amplifiers E and B, have their inputsconnected to the output of an electrical wave train generator 6,. Thisgenerator is identical to that of FIG. 1.

Amplifiers R and R have their respective inputs connected to therespective outputs of V and V Their respective outputs are connected torespective dispersive delay lines LD and LD identical to the delay lineLD of FIG. 1.

The outputs of these delay lines are respectively connected throughdiode means not shown respectively to the complementary triggeringinputs of a first bistable multivibrator BST 1. A master oscillator Pcontrols a timing circuit BT, which in turn controls the operatio ofgenerator G, as hereinabove described.

The output of bistable BST 1 is connected to the first input of a firstAND gate ETl, the output of which is connected to a first counter CTl,the read out of which is proportional to the velocity to be measured.

This part of the device operates as follows:

Under the triggering action of timing circuit BT and of generator G1,transducers V and V transmit simultaneously two frequency modulated wavetrains as in FIG. 1.

The upstream wave train travels from V to V and the downstream wavetrain travels from V to V the respective propagation times being T2 andT1, T2 being higher than Tl.

it can be shown, that if L is the distance separating transducers V fromV c being the sound velocity in the fluid,

v the velocity of the fluid to be measured, and 0 the angle between thetrajectory and the beam direction. As v is generally negligible comparedto c the difference between the upstream and downstream travel timeintervals can be written as:

T2- T1 (2 Lv cos 6)]0 The measurement of T2 T1 gives the value of v, ifcis known.

Bistable BSTl delivers a rectangular pulse voltage, the duration ofwhich is proportional to T2 T1. As a matter of fact, the result does notdepend from the delays introduced by the two identical delay lines;these delays being the same.

A second pair of transducers E and R are mounted, in the same way V andV for respectively transmitting and receiving a sonic beam perpendicularto the flow direction, said beam crossing the pipe along a diameterthereof.

The circuits associated with these transducers i.e. transmitter Ereceiver R delay line LD3, and bistable BST 3 are identical to those ofFIG. 1.

A second generator G3, controlled by timing circuit HT is connected totransmitter E3. Timing circuit ET is also connected to the settingtrigger input of the second bistable multivibrator BST 3, the resettinginput of which is connected to the output of delay line LD3 throughdiode means not shown.

As in F IG. 1, the second bistable multivibrator delivers a rectangularpulse voltage, the duration of which is T, and for which T- t D/c,

I being the delay time of the second delay line LD3, and D the diameterof the pipe.

The output of BST 3 is connected to a circuit arrangement capable ofgenerating a pulse train, having a repetition frequency which is alinear function of c Thus, the output of oscillator P is coupled to asecond AND gate ET3, the other input of which receives the outputrectangular voltage waveform of BST 3. The output of the gate ET3 isconnected to a counter C, This latter delivers, for each pulse received,an output voltage which is delivered in turn to a digitalto-analogueconverter D/A. This latter comprises a capacitor, the charge of which isa linear function of the number of pulses delivered by the counter. Atthe end of the count, the converter delivers a voltage V the value ofwhich is proportional to the count of counter C.

Bistable BST3 is in the state 1 during a time interval equal to 0/0 t.The end value of voltage V is as a consequence a linear function of He.

A squaring device Q, receives this voltage V and delivers a voltage U Vfunction of l/c This voltage is applied to the frequency control inputof a voltage controlled variable frequency pulse generator OSC, theoutput of which is connected to the other input of the first AND gateETl. The repetition frequency of the pulses delivered by the generatorOSC varies proportionally with 1/c The first counter CTl counts theselatter pulses during the time T2 T1.

The count displayed is equal to 2 LV cos 0; it is proportional to Vsince L and 0 are perfectly known.

The pulse compression technique makes it possible to considerablylengthen the duration of the transmitted wave train signals and thus tooperate in a quasistationary condition without, however, losing the timeresolution, because compression is carried out at the receiving end.

This technique is directly applicable to the measurement of thepropagation time over the transverse trajectory, that is to say to themeasurement of the ultrasonic velocity. It is likewise applicable to theoblique trajectories, that is to say to the measurement of the flowvelocity since it enables us to replace the sometimes delicate operationof measuring the phase, by a measurement of the delay between twoinstants which are perfectly established in time; these are in otherwords the instants of beginning of the transmission of the sonic wavetrain and that at which the received wave train is produced at theoutput of the delay line. Accurate measurement of the differenttransmission times across the fluid is thus possible without the need toresort to a phase measurement.

This method is of especial significance in the context of measuringpropagation times through gases.

What 1 claim, is:

1. An ultrasonic system for cyclically measuring the flow ofa fluid in apipe, comprising in combination:

first means for repeatedly generating a timing signal at the beginningof each measuring cycle;

second means triggered by said first means for generating a firstelectrical wave train of fixed duration, frequency modulated accordingto a predetermined law between fixed upper and lower frequencies,

at least a first pair of opposed transducer means for location onopposite sides of said pipe, including a first transducer for convertingsaid first wave train into a first sound wave and for transmitting saidfirst sound wave along a first path through the fluid within said pipeand a second transducer for receiving said transmitted first sound waveand for converting said received sound wave into a second electricalwave train;

first means for applying said first wave train to said first transducer;

first delay line means having a dispersive delay time versus frequencycharacteristic, fed by said second transducer for converting said secondelectrical wave train into a first compressed one of short duration;

first detector means fed by said first delay line means for delivering afirst compressed pulse in response to said first compressed wave train;

a first bistable multivibrator having a first triggering input forreceiving said timing signal and an output for delivering in responsethereto a non-zero value constant voltage and a second triggering inputfor receiving said first compressed pulse and for delivering at saidoutput in response thereto a zero value voltage, whereby said firstmultivibrator output delivers a first rectangular waveform having aduration equal to the sum of the sound wave propagation time intervalacross the fluid between said first and second transducers and theconstant delay time interval provided by said delay line means.

2. A system as claimed in claim 1, further comprising first means formeasuring the duration of said first rectangular waveform.

3. A system as claimed in claim 2, wherein said first means formeasuring comprises:

clock means having an output for delivering recurrent pulses;

a first AND gate having a first input coupled to said firstmultivibrator output, a second input coupled to said clock output and anoutput, and

first counter means having an input coupled to said first gate outputand an output for delivering a digital count corresponding to the numberof clock pulses transmitted by said first gate during said firstrectangular waveform.

4. A system as claimed in claim 3, wherein said first path isperpendicular to the flow direction, said system further comprising:

third means triggered by said first means for generating a thirdelectrical wave train of fixed duration, frequency modulated accordingto a predetermined law between fixed upper and lower frequencies;

a second pair of opposed transducer means for location on opposite sidesof said pipe on an axis obliquely inclined with respect to the flowdirection, including a third and a fourth transducer for alternatelysimultaneously converting said third wave train respectively into asecond and a third sound wave and for respectively transmitting saidsecond and third sound waves along said oblique axis in both theupstream and downstream directions, and for respectively receiving saidsecond and third sound waves and converting same into a fourth and afifth electrical wave train;

second means for applying said third electrical wave train to said thirdand fourth transducers;

second and third dispersive delay line means respectively fed by saidthird and fourth transducers, for respectively converting said third andfourth electrical wave trains into a second .and a third compressedones, of short duration;

second and third detector means respectively fed by said second andthird delay line means for respectively delivering a second and a thirdcompressed pulse in response to said second and third compressed wavetrains;

a second bistable multivibrator having a first triggering input forreceiving said second compressed pulse and an output for delivering inresponse thereto a non-zero value constant voltage, and a secondtriggering input for receiving said third compressed pulse and fordelivering at said output in response thereto a zero value voltage, saidsecond multivibrator output delivering a second rectangular waveform,whose duration is substantially equal to the difference between theupstream and downstream propagation time intervals of said sound waves;

and secondmeans for measuring the duration of said second rectangularwaveform.

5. A system as claimed in claim 4, wherein said clock means is made upfrom a master oscillator delivering constant frequency pulses andwherein said second measuring means comprises:

a digital-to-analog converter fed by the output of said first countermeans for delivering a voltage proportional to said di ital count; asquaring circuit fed y said converter for delivering a control voltageequal to the square of said pro portional voltage;

a voltage controlled variable frequency pulse generator having a controlinput fed by said control voltage and an output for delivering a pulsetrain whose repetition frequency is a linear function of said controlvoltage;

a second AND gate having a first input coupled to said secondmultivibrator output, a second input coupled to said variable frequencygenerator output, and an output;

second counter means having an input coupled to said second gate output,and an output for delivering a count proportional to the flow velocityof the fluid.

1. An ultrasonic system for cyclically measuring the flow of a fluid in a pipe, comprising in combination: first means for repeatedly generating a timing signal at the beginning of each measuring cycle; second means triggered by said first means for generating a first electrical wave train of fixed duration, frequency modulated according to a predetermined law between fixed upper and lower frequencies, at least a first pair of opposed transducer means for location on opposite sides of said pipe, including a first transducer for converting said first wave train into a first sound wave and for transmitting said first sound wave along a first path through the fluid within said pipe and a second transducer for receiving said transmitted first sound wave and for converting said received sound wave into a second electrical wave train; first means for applying said first wave train to said first transducer; first delay line means haviNg a dispersive delay time versus frequency characteristic, fed by said second transducer for converting said second electrical wave train into a first compressed one of short duration; first detector means fed by said first delay line means for delivering a first compressed pulse in response to said first compressed wave train; a first bistable multivibrator having a first triggering input for receiving said timing signal and an output for delivering in response thereto a non-zero value constant voltage and a second triggering input for receiving said first compressed pulse and for delivering at said output in response thereto a zero value voltage, whereby said first multivibrator output delivers a first rectangular waveform having a duration equal to the sum of the sound wave propagation time interval across the fluid between said first and second transducers and the constant delay time interval provided by said delay line means.
 2. A system as claimed in claim 1, further comprising first means for measuring the duration of said first rectangular waveform.
 3. A system as claimed in claim 2, wherein said first means for measuring comprises: clock means having an output for delivering recurrent pulses; a first AND gate having a first input coupled to said first multivibrator output, a second input coupled to said clock output and an output, and first counter means having an input coupled to said first gate output and an output for delivering a digital count corresponding to the number of clock pulses transmitted by said first gate during said first rectangular waveform.
 4. A system as claimed in claim 3, wherein said first path is perpendicular to the flow direction, said system further comprising: third means triggered by said first means for generating a third electrical wave train of fixed duration, frequency modulated according to a predetermined law between fixed upper and lower frequencies; a second pair of opposed transducer means for location on opposite sides of said pipe on an axis obliquely inclined with respect to the flow direction, including a third and a fourth transducer for alternately simultaneously converting said third wave train respectively into a second and a third sound wave and for respectively transmitting said second and third sound waves along said oblique axis in both the upstream and downstream directions, and for respectively receiving said second and third sound waves and converting same into a fourth and a fifth electrical wave train; second means for applying said third electrical wave train to said third and fourth transducers; second and third dispersive delay line means respectively fed by said third and fourth transducers, for respectively converting said third and fourth electrical wave trains into a second and a third compressed ones, of short duration; second and third detector means respectively fed by said second and third delay line means for respectively delivering a second and a third compressed pulse in response to said second and third compressed wave trains; a second bistable multivibrator having a first triggering input for receiving said second compressed pulse and an output for delivering in response thereto a non-zero value constant voltage, and a second triggering input for receiving said third compressed pulse and for delivering at said output in response thereto a zero value voltage, said second multivibrator output delivering a second rectangular waveform, whose duration is substantially equal to the difference between the upstream and downstream propagation time intervals of said sound waves; and second means for measuring the duration of said second rectangular waveform.
 5. A system as claimed in claim 4, wherein said clock means is made up from a master oscillator delivering constant frequency pulses and wherein said second measuring means comprises: a digital-to-analog converter fed by the output of said first counter means for deliverinG a voltage proportional to said digital count; a squaring circuit fed by said converter for delivering a control voltage equal to the square of said proportional voltage; a voltage controlled variable frequency pulse generator having a control input fed by said control voltage and an output for delivering a pulse train whose repetition frequency is a linear function of said control voltage; a second AND gate having a first input coupled to said second multivibrator output, a second input coupled to said variable frequency generator output, and an output; second counter means having an input coupled to said second gate output, and an output for delivering a count proportional to the flow velocity of the fluid. 